1. Field of the Invention
The present invention relates to a potter's wheel for working clay and other pottery material on a turntable to make pots, bowls, plates, cups and the like, and more particularly pertains to such a potter's wheel driven by a DC brushless motor.
2. Description of the Related Art
In the field of pottery, many people use an electrically driven potter's wheel of which turntable is driven by an electric motor. Such an electrically driven potter's wheel is provided with the turntable for supporting a work of wet clay and other material, an electric motor for driving the turntable, a pedal for adjustment of the motor speed, and a speed control for controlling the rotational speed of the motor as a function of amount of operation to the pedal, i.e. how much the pedal is depressed by a foot of a user or operator. Although pottery material other than clay can be used for the pottery, explanation will be made hereinafter with reference to clay as a representative of the material for the pottery. However, it is to be noted that the present invention is also applicable to other pottery material than clay.
Upon throwing pottery, a user deposits a mass of wet clay on the turntable and hand-shape the wet clay to a desired form while turning the turntable. During that throwing process, a force is imparted to the wet clay as the user accesses the clay, and the force acts as a load to the electric motor to vary the rotational speed of the motor. Such variation of motor speed is not preferable for the formation of the pottery. In order to maintain the motor speed constant, the user has to delicately adjust the amount of operation of the pedal and such adjustment requires expertise.
Further, a conventional potter's wheel of the type driven by a DC brushless motor is constructed to detect the change or switching of magnetic pole of the rotor magnet, by means of a Hall sensor and determine the timing for switching the direction of the electric current running through coils of a stator of the DC brushless motor. However, such a construction has a limit in rotating the turntable smoothly. Especially, when the speed of the rotor of the motor is in a low range, a lug or discordance occurs in synchronization between the switching of the direction of the electric current and rotation of the motor, causing step-out and stopping the motor instantaneously. The unexpected stop of the motor during the throwing of the pottery will result in destroy of the work which has been shaped.